Positive capacitive feedback to increase the slew rate of operational amplifiers is known. U.S. Pat. No. 4,701,720 teaches the use of positive capacitive feedback to increase the tail current of an input differential pair when the output slew is negative. The feedback increases the negative slew rate so that the positive and negative slew rates are comparable.
The primary disadvantage of all prior art operational amplifiers employing capacitive feedback to improve the slew rate is that the feedback capacitors are connected directly to the output. The amplifier is therefore loaded by the feedback capacitance and by parasitics associated with the feedback circuit. The output loading reduces the bandwidth and the phase margin of the amplifier, as well as reducing the maximum current which is delivered to the load.